The CommonWell Health Alliance has signed on one of the biggest ambulatory electronic health record vendors, the top healthcare IT advocacy organization, an image-sharing network and others to the private-sector interoperability group.

eClinicalWorks, a cloud-based EHR used by more than 115,000 physicians, has joined CommonWell as a contributor member and will commit to offering its interoperability services to its customers.

HIMSS, the global nonprofit organization focused on improving health through information technology – whose 2016 annual conference and exhibition kicks off in Las Vegas on Feb. 29 – will also join CommonWell as a general member.

[Also: CommonWell Health Alliance plans nationwide expansion]

Other new contributor members include lifeIMAGE, a medical image sharing network with 150,000 users and 1.5 billion exams exchanged; MediPortal, a developer of patient engagement tools, and Modernizing Medicine, whose clinical and financial technology is geared toward physician practices and ambulatory sites.

Other general members include ImageTrend, maker of Web-based emergency response and health information exchange technology, and Mana Health, a platform-as-a-service that links patient data from EHRs, apps and devices.

“The diversity in our membership is representative of our commitment to reach the full continuum of care and to help ensure pertinent patient information is available to patients and caregivers regardless of where care occurred," said Jitin Asnaani, executive director of CommonWell Health Alliance.

[Also: Epic trades jabs with CommonWell Health Alliance]

The addition of Westborough, Massachusetts-based eClinicalWorks – with some 70,000 facilities running its technology – is perhaps the biggest EHR get for CommonWell since MEDITECH signed on in April 2015.

CommonWell officials say alliance members represent 72 percent of the hospital EHR market and 34 percent of the ambulatory EHR market.

Still a hold out is Epic Systems, which boasts nearly 12 percent of EHR marketshare all on its own.

Twitter: @MikeMiliardHITN